Electrolytic grinder and method of grinding



Oct. 30, 1962 G. CROMPTON 3,061,529

ELECTROLYTIC GRINDER AND METHOD OF GRINDING Filed April 6, 1959 INVENTORrates Unite The invention relates to electrolytic grinders and methodsof grinding.

One object is to provide an electrolytic grinder capable of operatingwith a non-conductive grinding wheel. Precision grinding is now usuallydone using vitrified grinding wheels which are non-conductive. Someprecision grinding is done with organic bonded grinding wheels usuallyphenolic resin bonded grinding wheels and these are non-conductive.Other kinds of grinding are done with various organic bonded grindingwheels including phenolic resin bonded grinding wheels, also rubberbonded grinding wheels and some others. In most grinding operations thegrinding wheel is non-conductive. For certain grinding operations suchas the grinding of the hard cemented carbides, metal bonded diamondWheels are used. These are conductive. But in most grinding operations,covering by far the greater part of all grinding, conductive grindingwheels cannot be efliciently used. Another object is to provide a methodof grinding which can be performed with a non-conductive grinding Wheel.

Another object of the invention is to provide an electrolytic grinder ofsimple construction. Another object is to provide a method ofelectrolytic grinding which can be carried out with simple apparatus.Another object of the invention is to achieve efiicient electrolyticgrinding of steels, cast iron, non-ferrous metals and to multiply thestock removal rate as much as several fold in a given time. Anotherobject is to achieve the foregoing object without causing any greaterwheel wear and in some cases less wheel wear. Another object is, bymeans of a very simple circuit involving no electronic apparatus andwith no mechanical complexities and with an ordinary grinding wheel,completely to avoid all arcing and sparking, the former being in allcases and the latter when it is strong, detrimental in electrolyticgrinding. The foregoing is actually six objects which are achieved inthis invention.

Other objects will be in part obvious or in part pointed outhereinafter.

The accompanying drawing illustrating one of many possible embodimentsof the invention is a view of a cylindrical grinder partly in endelevation and partly in vertical section.

As conducive to a clearer understanding of the present invention, it isnoted that electrolytic grinding of the hard cemented carbides is now anindustrial fact. Industrially the grinding wheels have always been metalbonded wheels, mostly metal bonded diamond Wheels but occasionally metalbonded silicon carbide wheels. It has been found that the saving indiamonds by electrolytic grinding of the hard cemented carbides runs ashigh as 90%, meaning that for a given amount of stock removal only onetenth as much wheel wear is incurred as in the same grinding operationwithout the assistance of the electrolytic work erosion. Of course inmany cases the saving isnt this great.

Although this invention is illustrated as applied to a cylindricalgrinder, it has no such limitation as it can be embodied in any otherkind of a precision grinder, such as a surface grinder, a centerlessgrinder and any other type and also in non-precision grinders of variouskinds wherever liquid coolant based on water can be used.

P! 3,051,529 Patented Oct. 30, 1962 Referring to the drawing, themachine has a base 11 having ways supporting a carriage 12 whichsupports a work table 13 having ways which supports a headstock 14supporting a motor 15 which through driving mechanism rotates a faceplate 16.

A grinding wheel is supported and rotated by a spindle 21 which isjournalled in a wheel head not shown on a cross slide not shown, thespindle being driven by a motor not shown through pulleys and belts. Allthis is conventional and does not have to be illustrated. The crossslide will usually be given an infeed and withdrawal movement byhydraulic mechanism and also can be operated by a hand wheel 25.

The grinding wheel 20 can be any kind of an electrically non-conductivegrinding wheel in accordance with the foregoing discussion. It couldeven be a metal bonded grinding wheel so far as operability is concernedbut there is nopresent apparent advantage therein, in fact this wouldcancel one of the objects of the invention. Still, for the grinding ofhard carbide with metal bonded diamond wheels the present method ofproducing electrolytic work erosion may be preferred.

In the base 11 is formed a tank lined with rubber 31 or othernon-conductive material. This contains water having dissolved thereinsome non-corrosive salt to make it electrically conducting. Alkalinesalts can be used for ferrous metal grinding. Very good examples aresodium carbonate Na CO sodium phosphates and sodium borate, Na B ONeutral salts can be used in some cases, the common eaxmple being sodiumchloride. Even acids can be used for certain grinding operations wherediscoloration of the work is not important and where erosion of machineparts can be tolerated in view of the further disintegration of themetal being ground by the acid. Bases such as sodium hydroxide can beused. In any case where sodium is a part of the compound other alkalimetals such as potassium can be substituted, also alkaline earth metals,where soluble salt results. In fact there is no limit to the materialswhich can be used provided they are readily soluble in water ionizingtherein. But for most practical grinding operations, the salt should bealkaline. The three specifically mentioned are rust inhibitors which isan advantage and they are also noncorrosive to the hands. Broadlyspeaking, therefore, the electrolyte used in accordance with thisinvention is any water based electrolyte having ionized material thereintherefore being a conductor of electricity. All kinds of mixtures can beused. I

The electrolyte is pumped through insulated piping to a metal nozzle 40whence it emerges in a stream 41 to contact the work piece 42 actingboth as a coolant, a grinding swarf remover and an electrolyte to conveythe positive electricity from the work piece thus producing electrolyticwork erosion at the same time that the grinding wheel 20 is abrasivelygrinding the work piece 42. I will first describe thecoolant-electrolyte circuit and then the electric circuit.

In the tank 30 is an electric motor 45 driving a pump unit 46 having aself-contained strainer to remove the abrasive swarf. This pump 46 pumpselectrolyte 35, which will be called water from now on because it ismostly water, through a metal pipe 50 which is connected by a clamp 51to a rubber hose 52 which is connected by a clamp 53 to a plastic pipe54 which is supported by a bracket 55 which is secured to the wheelguard 56. The plastic pipe 54 is connected to a valve 58 having anoperating handle 59 which is connected to a swivel joint 60 which ishollow for the passage of the water which is connected to a pipe 61which is connected to the metal nozzle 40.

The grinding wheel 20 is usually not as wide as the work piece 42 andeven if it is, the water can go down ward on either side of the wheel 29where it flows into a chamber 65 formed by various walls of the machinebase and having a perforated bottom 66 over the tank 30, so thereforethe water returns to the tank to be repumped around the circuit again.

Any source of electric current can be used but there is shown arectifier 70 energized by a cable 71 supplying electricity from theregular factory single phase system. Usually this will be a cycle 440volt supply. This cable is connected to a switch box 72 having a doublepole switch 73 operable on the outside of the machine anddiagrammatically shown in the drawing which is connected to the 440 voltline 75.

From the positive side of the output of the rectifier goes a cable to aninsulated brush 81 in an insulat ing holder 82 secured to the headstock14 which holder has a spring 83 pressing the brush 81 against theperiphery of the face plate 16 which is of course made of metal. Thusthe direct current reaches the face plate 16 and then passes into a workdriving dog 84- which drives a clamp 85 which grips the work piece 42 todrive it. This clamp 85 is broken away in the upper left quadrant toshow the stream 41.

The electric current now flows up the stream 41 to the nozzle 40 and dueto the greater conductivity of the nozzle most of the electricity goesinto it at the very opening of the nozzle. If this nozzle is made ofbrass or copper, its resistance from a practical point of view is zero.

Clamped by clamp to the nozzle 40 is a cable 91 which is flexible toallow for movement of the wheel slide and this cable 91 is secured to astandard 92 secured to the far end of the wheel base 11. The cable 91extends to an exteriorly operated switch 93 in a switch box 94 which isconnected to a cable 95 connected to the negative side of the rectifier7 0. Thus from the nozzle 40 electricity flows through the cable 91 tothe switch 93 through the cable 95 to the negative side of the rectifier70. All cables mentioned herein are of course suitably insulated.

In the supplement to the report on Electrolytic Process for ShapingMetals and Metal Carbides published in or about December 1951, by GeorgeF. Keeleric of United Drill and Tool Corp, Howard T. Francis of ArmourResearch Foundation and Charles L. Faust of Battelle Memorial Institute,a table of electrolytic grinding is given wherein the highest currentused was 38 amperes.

As progress has been made since then I assume that it will be desirableto provide at least 40 amperes of current. In a practical grindingoperation the stream 41 of water may be 5 centimeters long. It should bein the form of a ribbon which in a given grinding operation might be 4centimeters wide and one centimeter thick. The resistivity of watercontaining 15 grams of sodium carbonate for grams of Water at 18 C., 64F., is 12 ohms cm. The cross section at the orifice of the nozzle 40 istherefore 4 square centimeters and it can be assumed not to changealthough it increases somewhat. The resistance of the stream istherefore 12 A=15 ohms. The rest of the circuit can be disregardedespecially as, since the stream 41 widens, the resistance will be alittle less than 15 ohms. Using the equation C=E/R we have 40=E/15 andE=600 volts.

This might seem to be prohibitively dangerous but it is not for thefollowing reasons. The positive side of the output of the rectifier 70is grounded because the face plate 16 is grounded to the machine exceptfor an oil film in the spindle bearings and this kind of a grinder musthave a tail center and a tail stock which tail center contacts the workpiece and sometimes there is no oil film between them. Even if the oilon the ways of the base supporting the carriage 12 is an insulator, theoperator working on the machine will at one time or another touch theheadstock 14 or the tail stock or the table 13.

But he cannot receive a shock unless he also touches the negative sideof the line somewhere.

The nozzle 40 should be given a coating of Rokide (trademark) by meansof the Rokide process patented to Wheildon #2,707,691. This coating isactually a porous coating of oxide commercially one of either aluminumoxide or zirconium oxide or in a few cases zircon, all of which are goodinsulators. This is done after the clamp is applied and the clamp alsois given a Rokide coating. The pipe 61 is made of some non-conductivematerial, for example a strong plastic. Over the Rokide coating to fillthe pores it is desirable to apply any penetrating organic materialwhich will stay when the solvent dries such as shellac and alcohol. Athin solution should be used to obtain good penetration. After the cable91 is connected to the clamp 90 the connection should be Rokided andthis can be done because the Rokide apparatus is portable. Then theconnection should be shellaced.

No appreciable current will run to the gate valve 58 through the waterbecause the regular path of the current is a far, far better conductorthan the water. Since the work piece 42 is so much better a conductorthan the human body it is probable that a finger could be put into thestream 41 without a serious burn but of course it shouldnt be tried.Water mist and drops of water cannot carry any electricity hence areharmless. For this reason also practically no electricity is carrieddownward beyond the work piece 42 by the water because before it touchesmetal parts of the machine below the work piece it is in the form ofseparate drops.

It will be seen that yielding 40 amperes current, the rec tifier musthave an output of 24 kilowatts and an input of a little more say 25kilowatts. At 440 volts, to get 25 kilowatts the current will be 56.82amperes. Good sized cable is therefore needed both for the input and theoutput of the rectifier and in that respect the drawing must beconsidered merely diagrammatic. Rectifiers having an input of 25kilowatts and even larger are readily available. In fact rectifiershaving an output of 30 kilowatts are now being used for some purposesand probably there are even larger ones. To make the machine still moreetficient as an electrolytic grinder since it is relatively safe asshown, the current used could be increased as much as five fold byreducing the length of the stream 41 to one centimeter.

The rectifier box should also have in it a transformer to transform theinput from 440 volts to, for example, 600 volts or any other desiredE.M.F. plus suitable breaker switches for overload and an operatingswitch for the input or this can be in the cable 71 as shown. It mayhave an ammeter and a voltmeter for the input and the output.

A special feature of the invention is that using the stream 41 for whatcan be called the electrode in electrolytic grinding, there can beneither arcing nor sparking with any reasonable current density so faras I am aware. This is because the electrode stream 41 is in actualcontact with the other electrode, work piece 42. The stream would quenchany are that started and there is no gap for a spark. Furthermore thecurrent cannot channel; it is evenly distributed. This offers aconsiderable improvement in electrolytic grinding and for some purposesgives better finishes.

By providing two swivel joint instead of the single swivel joint 60, thenozzle 40 can be pressed into contact with the grinding wheel 20 and thework piece 42. The grinding wheel will immediately grind it on one sideuntil contact is broken and when the current is turned on an arc will beformed which will make a small gap on the other side. This arcing willbe harmless as the work piece will be ground later.

The circuit breakers may work several times but after a while a veryfine gap is formed. If this is only as small as one millimeter, and itmight be less, the resistance is reduced to one-tenth of what it was atthe last calculation which was one-fifth of what it was at the firstcalculation, that is the resistance is reduced to three-tenths of anohm. Thus with a voltage of 600 and a resistance of three-tenths of anohm, the current is 2,000 amperes.

While grinding keeps the work piece round or flat or some other shape toaccuracy and a grinding machine brings the work piece to precision size,the electrolytic method of eroding metal herein described may haveadvantages in certain cases where there i no grinding involved. Thecharged stream 41 erodes the metal and also carries away dislodged metalparticles which are filtered out by the filter or strainer in the pumpunit 46.

It will thus be seen that there has been provided by this inventionelectrolytic grinders and methods of grinding in which the variousobjects hereinabove set forth together with many thoroughly practicaladvantages are successfully achieved. As many possible embodiments maybe made of the above invention and as many changes might be made in theembodiments above set forth, it is to be understood that all matterhereinbefore set forth, or shown in the accompanying drawing, is to beinterpreted as illustrative and not in a limiting sense.

For the best mode of the invention so far as the electrolyte isconcerned, I pick alkaline salts and of those, since I know itsresistivity but do not know that of the others, I pick sodium carbonate.The invention can be applied to many diflerentkinds of grinders each onebeing the best for some grinding operations so the best mode cannot bepicked but to comply with the statute I pick the mechanism described.

I claim:

1. An electrolytic grinder comprising a base, a grinding wheel, means torotate said grinding wheel supported by said base, a work piece holdersupported by said base and positioned to hold an electrically conductivework piece in contact with said grinding wheel, a fluid circulatingsystem electrically insulated from said base including circulating meansoperable to continuously circulate an electrically conductive fluid andan electrically conductive nozzle from which a continuous stream ofelectrically conductive fluid is discharged for impingement upon a Workpiece at its point of contact with said grinding wheel, and anelectrical circuit electrically insulated from said base including asource of direct current, an electrical conduit interconnecting thepositive side of said source and said work piece holder so as to rendersaid work piece holder and an electrically conductive work piecesupported thereby positive, and an electrical conduit interconnectingthe negative side of said source and said nozzle so as to render saidnozzle and a stream of electrically conductive fluid in contact with anddischarged therefrom negative.

2. An electrolytic grinder comprising a base, a grinding wheel, means torotate said grinding wheel, an electrically conductive work piece holdersupported by said base and positioned to hold an electrically conductivework piece in contact with said grinding wheel, a fluid circulatingsystem supported by and electrically insulated from said base havingcirculating means incorporated therein for circulating an electrolyticfluid therethrough, said fluid circulating system including anelectrically conductive nozzle arranged to be continuously supplied witha circulating electrolytic fluid by said circulating means andpositioned to direct a jet of electrolytic fluid substantiallytangentially of the grinding Wheel at its point of contact with a workpiece, a source of direct current, an electrical conduit interconnectingsaid source and said work piece holder so as to render said work pieceholder positive, and an electrical conduit interconnecting said sourceof direct current and said nozzle to render said nozzle negative,whereby an electrical circuit for electrolytically assisted grinding isestablished and maintained by the impingement upon an electricallyconductive work piece of a continuous stream of electrolyte dischargedfrom an electrically conductive nozzle independent of the electricalproperties of the grinding wheel.

3. An electrolytic grinder comprising a base, a grinding wheel, means torotate said grinding wheel supported by said base, an electricallyconductive work piece holder supported by said base and positioned tosupport an electrically conductive work piece in engagement with saidgrinding wheel, a fluid circulating system for an electrolytic-coolantfluid supported by and insulated from said base including means forcirculating electrolytic-coolant fluid Within said system and anelectrically conductive nozzle for discharging a continuous stream ofelectrolyticcoolant fluid so that the continuous stream dischargedimpinges on the portion of the surface of a work piece supported by saidwork piece holder contiguous to said grinding wheel, and means togethercomprising an electrical circuit including a source of direct electriccurrent provided with positive and negative terminals, an electricalconduit interconnecting the positive terminal of said source and saidwork piece holder to render said work piece holder and thence anelectrically conductive work piece supported thereby positive, and anelectrical conduit interconnecting the negative terminal of said sourceand said nozzle to render said nozzle and thence a continuous stream ofelectrolytic-coolant fluid discharged therefrom negative.

4. The method of combined grinding and electrolytic erosion whichcomprises providing a water based electrolyte having ionized materialtherein which is a conductor of electricity, causing said electrolyte toflow through an electrically conductive nozzle as a continuous streamfrom an external source against the contiguous surfaces of a grindingwheel and an electrically conductive work piece engaged thereby,energizing a work piece so disposed positively electrically, energizingsaid nozzle and thence the continuous stream of electrolyte dischargedtherefrom negatively electrically, and coincidentally grinding a workpiece so disposed with a grinding wheel, thereby electrolyticallyeroding the work piece and also abrasively grinding it.

5. An electrolytic grinder according to claim 1 in which the grindingwheel is an electrically non-conductive Wheel.

6. Method of grinding according to claim 4 in which the ionized materialis an alkaline salt.

References Cited in the file of this patent UNITED STATES PATENTS1,416,929 Bailey May 22, 1922 1,473,060 Taylor Nov. 6, 1923 2,061,554Billiter Nov. 24, 1936 2,385,198 Engle Sept. 18, 1945 2,741,594Bowersett Apr. 10, 1956 2,793,992 Heuser May 28, 1957 2,798,846 ComstockJuly 9, 1957 2,826,540 Keeleric Mar. 11, 1958 2,873,232 Zimmerman Feb.10, 1959 2,961,394 Williams Nov. 22, 1960 FOREIGN PATENTS 748,485 GreatBritain May 2, 1956

4. THE METHOD OF COMBINED GRINDING AND ELECTROLYTIC EROSION WHICHCOMPRISES PROVIDING A WATER BASED ELECTROLYTE HAVING IONIZED MATERIALTHEREIN WHICH IS A CONDUCTOR OF ELECTRICITY, CAUSING SAID ELECTROLYTE TOFLOW THROUGH AN ELECTRICALLY CONDUCTIVE NOZZLE AS A CONTINUOUS STREAMFROM GRINDING WHEEL AND AN ELECTRICALLY CONDUCTIVE WORK PIECE GRINDINGWHEEL AND AN ELECTRICALLY CONDUCTIVE WORK PIECE ENGAGHED THERBY,ENERGIZING A WORK PIECE SO DISPOSED POSITIVELY ELECTRICALLY, ENERGIZINGSAID NOZZLE AND THENCE THE CONTINUOUS STREAM OF ELECTROLYTE DISCHARGEDTHEREFROM NEGATIVELY ELECTRICALLY, AND COINCIDENTALLY GRINDING A WORKPIECE SO DISPOSED WITH A GRINDING WHEEL, THEREBY ELECTROLYTICALLYERODING THE WORK PIECE AND ALSO ABRASIVELY GRINDING IT.